US20150028866A1 - Vapor cell structure having cavities connected by channels for micro-fabricated atomic clocks, magnetometers, and other devices - Google Patents
Vapor cell structure having cavities connected by channels for micro-fabricated atomic clocks, magnetometers, and other devices Download PDFInfo
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- US20150028866A1 US20150028866A1 US13/948,888 US201313948888A US2015028866A1 US 20150028866 A1 US20150028866 A1 US 20150028866A1 US 201313948888 A US201313948888 A US 201313948888A US 2015028866 A1 US2015028866 A1 US 2015028866A1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/02—Measuring direction or magnitude of magnetic fields or magnetic flux
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/02—Measuring direction or magnitude of magnetic fields or magnetic flux
- G01R33/032—Measuring direction or magnitude of magnetic fields or magnetic flux using magneto-optic devices, e.g. Faraday or Cotton-Mouton effect
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- G—PHYSICS
- G04—HOROLOGY
- G04F—TIME-INTERVAL MEASURING
- G04F5/00—Apparatus for producing preselected time intervals for use as timing standards
- G04F5/14—Apparatus for producing preselected time intervals for use as timing standards using atomic clocks
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S1/00—Masers, i.e. devices using stimulated emission of electromagnetic radiation in the microwave range
- H01S1/06—Gaseous, i.e. beam masers
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T137/00—Fluid handling
- Y10T137/8593—Systems
Definitions
- This disclosure is generally directed to gas cells. More specifically, this disclosure is directed to a vapor cell structure having cavities connected by channels for micro-fabricated atomic clocks, magnetometers, and other devices.
- MFACs micro-fabricated atomic clocks
- MFAMs micro-fabricated atomic magnetometers
- CsN 3 cesium azide
- N 2 cesium vapor and nitrogen gas
- This disclosure provides a vapor cell structure having cavities connected by channels for micro-fabricated atomic clocks, magnetometers, and other devices.
- an apparatus in a first example, includes a vapor cell having first and second cavities fluidly connected by multiple channels.
- the first cavity is configured to receive a material able to dissociate into one or more gases that are contained within the vapor cell.
- the second cavity is configured to receive the one or more gases.
- the vapor cell is configured to allow radiation to pass through the second cavity.
- a system in a second example, includes a vapor cell and an illumination source.
- the vapor cell includes first and second cavities fluidly connected by multiple channels.
- the first cavity is configured to receive a material able to dissociate into one or more gases that are contained within the vapor cell.
- the second cavity is configured to receive the one or more gases.
- the illumination source is configured to direct radiation through the second cavity.
- an apparatus in a third example, includes a vapor cell having a first wafer with first and second cavities and a second wafer with one or more channels fluidly connecting the cavities.
- the first cavity is configured to receive a material able to dissociate into one or more gases that are contained within the vapor cell.
- the second cavity is configured to receive the one or more gases.
- the vapor cell is configured to allow radiation to pass through the second cavity.
- FIGS. 1 through 4 illustrate an example vapor cell structure in accordance with this disclosure
- FIGS. 5 and 6 illustrate another example vapor cell structure in accordance with this disclosure
- FIGS. 7 and 8 illustrate example devices containing at least one vapor cell structure in accordance with this disclosure.
- FIG. 9 illustrates an example method for forming a vapor cell structure in accordance with this disclosure.
- FIGS. 1 through 9 discussed below, and the various examples used to describe the principles of the present invention in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the invention. Those skilled in the art will understand that the principles of the present invention may be implemented in any suitable manner and in any type of suitably arranged device or system.
- FIGS. 1 through 4 illustrate an example vapor cell structure 100 in accordance with this disclosure.
- the vapor cell structure 100 can be used, for example, to receive an alkali-based material (such as cesium azide) and to allow dissociation of the alkali-based material into a metal vapor and a buffer gas (such as cesium vapor and nitrogen gas).
- an alkali-based material such as cesium azide
- a buffer gas such as cesium vapor and nitrogen gas
- the vapor cell structure 100 includes a bottom wafer 102 , a middle wafer 104 , and a top wafer 106 .
- the bottom wafer 102 generally represents a structure on which other components of the vapor cell structure 100 can be placed.
- the bottom wafer 102 is also substantially optically transparent to radiation passing through the vapor cell structure 100 during operation of a device, such as a micro-fabricated atomic clock, magnetometer, or other device.
- the bottom wafer 102 can be formed from any suitable material(s) and in any suitable manner.
- the bottom wafer 102 could, for instance, be formed from borosilicate glass, such as PYREX or BOROFLOAT glass.
- the middle wafer 104 is secured to the bottom wafer 102 , such as through bonding.
- the middle wafer 104 includes multiple cavities 108 - 110 through the middle wafer 104 .
- Each cavity 108 - 110 could serve a different purpose in the vapor cell structure 100 .
- the cavity 108 can receive a material to be dissociated, such as cesium azide (CsN 3 ) or other alkali-based material.
- the cavity 108 can be referred to as a “reservoir cavity.”
- the cavity 110 can receive gas from the cavity 108 , such as a metal vapor and a buffer gas. Laser illumination or other illumination could pass through the cavity 110 during operation of a device, such as a micro-fabricated atomic clock, magnetometer, or other device.
- the cavity 110 can be referred to as an “interrogation cavity.”
- Each channel 112 fluidly connect the cavities 108 - 110 in the vapor cell structure 100 .
- Each channel 112 represents any suitable passageway through which gas or other material(s) can flow.
- there are three channels 112 although the vapor cell structure 100 could include two or more than three channels 112 .
- the channels 112 here are generally straight, have equal lengths, and are parallel to one another. However, the channels 112 could have any other suitable form(s).
- the middle wafer 104 could be formed from any suitable material(s) and in any suitable manner.
- the middle wafer 104 could represent a silicon wafer, and the cavities 108 - 110 and the channels 112 could be formed in the silicon wafer using one or more wet etches or other suitable processing techniques.
- the channels 112 could be formed in a silicon wafer using a potassium hydroxide (KOH) wet etch.
- KOH potassium hydroxide
- the etch of the silicon wafer could also be performed in a self-limiting manner, meaning the etch stops itself at or around a desired depth. For instance, when a narrow mask opening is used to expose the silicon wafer and the etching occurs at a suitable angle (such as about 54.74°), the etching can self-terminate before it etches completely through the silicon wafer.
- Each cavity 108 - 110 and channel 112 could have any suitable size, shape, and dimensions. Also, the relative sizes of the cavities 108 - 110 and channels 112 shown in FIGS. 1 through 3 are for illustration only, and each cavity 108 - 110 or channel 112 could have a different size relative to the other cavities or channels. Further, the relative depth of each channel 112 compared to the depth(s) of the cavities 108 - 110 is for illustration only, and each cavity 108 - 110 and channel 112 could have any other suitable depth. In addition, while each cavity 108 - 110 is shown as being formed completely through the wafer 104 , each cavity 108 - 110 could be formed partially through the wafer 104 .
- the top wafer 106 is secured to the middle wafer 104 , such as through bonding.
- the top wafer 106 generally represents a structure that caps the cavities 108 - 110 and channels 112 of the middle wafer 104 , thereby helping to seal material (such as gas) into the vapor cell structure 100 .
- the top wafer 106 is also substantially optically transparent to radiation passing through the vapor cell structure 100 during operation of a device, such as a micro-fabricated atomic clock, magnetometer, or other device.
- the top wafer 106 can be formed from any suitable material(s) and in any suitable manner.
- the top wafer 106 could, for instance, be formed from borosilicate glass, such as PYREX or BOROFLOAT glass.
- a portion 114 of the top wafer 106 could be thinner than the remainder of the top wafer 106 . This may help to facilitate easier UV irradiation of material placed inside the reservoir cavity 108 .
- any wafer 102 - 106 in the vapor cell structure 100 could have a non-uniform thickness at any desired area(s) of the wafer(s).
- the portion 114 of the top wafer 106 could have any suitable size, shape, and dimensions and could be larger or smaller than the reservoir cavity 108 .
- the portion 114 of the top wafer 106 could be thinned in any suitable manner, such as with a wet isotropic etch.
- the bottom and middle wafers 102 - 104 could be secured together, and the middle wafer 104 can be etched to form the cavities 108 - 110 and the channels 112 (either before or after the bottom and middle wafers 102 - 104 are secured together).
- An alkali-based material 116 (such as cesium azide) or other material(s) can be deposited into the reservoir cavity 108 as shown in FIGS. 3 and 4 . Any suitable deposition technique can be used to deposit the material(s) 116 into the cavity 108 .
- the top wafer 106 can be secured to the middle wafer 104 once the material 116 is placed in the cavity 108 . At this point, the cavities 108 - 110 and the channels 112 can be sealed.
- At least a portion of the material 116 in the cavity 108 can be dissociated. This could be accomplished by exposing the material 116 in the cavity 108 to ultraviolet (UV) radiation.
- UV radiation For example, an alkali-based material 116 can be dissociated into a metal vapor and a buffer gas.
- cesium azide could be dissociated into cesium vapor and nitrogen gas (N 2 ). Note, however, that other mechanisms could be used to initiate the dissociation, such as thermal dissociation.
- the dissociation of the material 116 creates gas inside the reservoir cavity 108 , which can flow into the interrogation cavity 110 through the channels 112 .
- the material 116 can be placed in one cavity 108 and dissociated, and the resulting gas can be used in a different cavity 110 during device operation.
- an illumination source 118 such as a vertical-cavity surface-emitted laser (“VCSEL”) or other laser, could direct radiation through the interrogation cavity 110 . Even if residue exists in the reservoir cavity 108 , it may not interfere with the optical properties in the cavity 110 .
- VCSEL vertical-cavity surface-emitted laser
- channels 112 also helps to ensure that vapor can travel from the reservoir cavity 108 into the interrogation cavity 110 , even if one or more channels 112 become blocked by debris or other material(s).
- the channels 112 could represent self-height-eliminating channels fabricated using a wet etch, rather than a more expensive and time-consuming dry etch. This can help to simplify the manufacture of the vapor cavity structure 100 .
- thinning the portion 114 of the top wafer 106 through which UV radiation is directed into the reservoir cavity 108 allows for enhanced dissociation of the material 116 in the cavity 108 (possibly at reduced power levels) while maintaining the mechanical integrity of the overall device.
- FIGS. 1 through 4 illustrate one example of a vapor cell structure 100
- the vapor cell structure 100 need not include two cavities and could include three or more cavities.
- the cavities 108 - 110 and channels 112 need not be arranged linearly, and the channels 112 need not be straight. Any arrangement of cavities connected by channels could be used, including non-linear and multi-level arrangements.
- the vapor cell structure 100 could be used with any other material(s) and is not limited to alkali-based materials or metal vapors and buffer gases.
- the vapor cell structure 100 can be used in any other suitable manner and is not limited to the use shown in FIG. 4 .
- FIGS. 5 and 6 illustrate another example vapor cell structure 500 in accordance with this disclosure.
- the vapor cell structure 500 shown here is similar in structure to that shown in FIGS. 1 through 4 .
- Reference numerals 102 - 110 and 114 - 118 are used here to denote structures that may be the same as or similar to structures described above. In this example, however, channels are not formed in the middle wafer 104 . Rather, one or more channels 512 are formed in the top wafer 106 .
- the top wafer 106 in this example may be said to represent a “capping” layer since it can be secured to the middle wafer 104 after the material 116 is inserted into the cavity 108 , thereby capping the structure 500 .
- the channels 512 can be etched into the top wafer 106 in any suitable manner.
- a photoresist mask can be formed on the top wafer 106 , patterned, and baked/cured.
- An isotropic wet etch such as one using a hydrofluoric acid (HF) dip, can then be performed to etch exposed portions of the top wafer 106 .
- the composition of the wet etch bath and the etch time can be selected to reduce the thickness of the top wafer 106 as desired.
- the photoresist layer can then be removed, and the top wafer 106 can be cleaned in preparation for securing to the middle wafer 104 .
- the top wafer 106 need not be thinned significantly or at all over the interrogation cavity 110 , helping to preserve the mechanical strength of the vapor cell structure 500 .
- the channels 512 in the capping layer can also serve other functions, such as by serving as condensation sites in the vapor cell structure 500 .
- FIG. 6 illustrates various examples of the channels and cavity portions that can be etched into a capping layer, such as the top wafer 106 .
- arrangement 602 includes portions of two unequally-sized cavities and a single channel between the cavities.
- Arrangement 604 includes portions of two unequally-sized cavities and two channels between the cavities.
- Arrangement 606 includes portions of two equally-sized cavities and three channels between the cavities.
- Arrangement 608 includes portions of two unequally-sized cavities and four channels between the cavities.
- Arrangement 610 includes portions of three unequally-sized cavities and five channels coupling each adjacent pair of cavities.
- Arrangement 612 includes portions of three equally-sized cavities and five channels coupling each adjacent pair of cavities.
- the top wafer 106 could be formed from borosilicate glass, and the etch of the top wafer 106 could occur using a hydrofluoric acid (BHF) bath.
- BHF hydrofluoric acid
- a hard mask could be used to mask the top wafer 106 . Any suitable etch, hard mask, and etch depth could also be used.
- FIGS. 5 and 6 illustrate another example of a vapor cell structure 500
- the vapor cell structure 500 could include any number of cavities and any number of channels in any suitable arrangement.
- the vapor cell structure 500 could be used with any suitable material(s) and is not limited to alkali-based materials or metal vapors and buffer gases.
- the vapor cell structure 500 can be used in any other suitable manner.
- FIGS. 7 and 8 illustrate example devices containing at least one vapor cell structure in accordance with this disclosure.
- a device 700 represents a micro-fabricated atomic clock or other atomic clock.
- the device 700 here includes one or more illumination sources 702 and a vapor cell 704 .
- Each illumination source 702 includes any suitable structure for generating radiation, which is directed through the vapor cell 704 .
- Each illumination source 702 could, for example, include a laser or lamp.
- the vapor cell 704 represents a vapor cell structure, such as the vapor cell structure 100 or 500 described above.
- the radiation from the illumination source(s) 702 passes through the interrogation cavity 110 of the vapor cell 704 and interacts with the metal vapor.
- the radiation can also interact with one or more photodetectors that measure the radiation passing through the interrogation cavity 110 .
- photodetectors can measure radiation from one or more lasers or lamps.
- Signals from the photodetectors are provided to clock generation circuitry 706 , which uses the signals to generate a clock signal.
- clock generation circuitry 706 uses the signals to generate a clock signal.
- the signal generated by the clock generation circuitry 706 could represent a highly-accurate clock.
- the signals from the photodetectors are also provided to a controller 708 , which controls operation of the illumination source(s) 702 .
- the controller 708 helps to ensure closed-loop stabilization of the atomic clock.
- a device 800 represents a micro-fabricated atomic magnetometer or other atomic magnetometer.
- the device 800 here includes one or more illumination sources 802 and a vapor cell 804 .
- Each illumination source 802 includes any suitable structure for generating radiation, which is directed through the vapor cell 804 .
- Each illumination source 802 could, for example, include a laser or lamp.
- the vapor cell 804 represents a vapor cell structure, such as the vapor cell structure 100 or 500 described above.
- the radiation from the illumination source(s) 802 can pass through the interrogation cavity 110 of the vapor cell 804 and interact with the metal vapor.
- the radiation can also interact with one or more photodetectors that measure the radiation passing through the interrogation cavity 110 .
- photodetector(s) can measure radiation from one or more lasers or lamps.
- Signals from the photodetector(s) are provided to a magnetic field calculator 806 , which uses the signals to measure a magnetic field passing through the interrogation cavity 110 .
- the magnetic field calculator 806 here is capable of measuring extremely small magnetic fields.
- the signals from the photodetector(s) can also be provided to a controller 808 , which controls operation of the illumination source(s) 802 .
- FIGS. 7 and 8 illustrate examples of devices 700 and 800 containing at least one vapor cell structure
- various changes may be made to FIGS. 7 and 8 .
- the devices 700 and 800 shown in FIGS. 7 and 8 have been simplified in order to illustrate example uses of the vapor cell structures 100 and 500 described above.
- Atomic clocks and atomic magnetometers can have various other designs of varying complexity with one or multiple vapor cell structures.
- FIG. 9 illustrates an example method 900 for forming a vapor cell structure in accordance with this disclosure.
- multiple cavities are formed in a middle wafer of a vapor cell structure at step 902 .
- This could include, for example, forming cavities 108 - 110 in a silicon wafer or other middle wafer 104 .
- Any suitable technique could be used to form the cavities, such as a wet or dry etch.
- One or more channels are formed in the middle wafer or a top wafer of the vapor cell structure at step 904 .
- This could include, for example, forming one or more channels 112 in the silicon wafer or other middle wafer 104 .
- This could also include forming one or more channels 512 in the top wafer 106 or other capping layer. Any suitable technique could be used to form the channels, such as a wet etch.
- the formation of the cavities and channels could also overlap, such as when the same etch is used to form both the cavities 108 - 110 and the channels 112 .
- a portion of the top wafer is thinned at step 906 .
- This could include, for example, etching a portion 114 of the top wafer 106 in an area adjacent to the reservoir cavity 108 . Any suitable etch can occur here, such as an isotropic wet etch.
- the formation of channels in the top wafer and the thinning of the top wafer could also overlap, such as when the same etch is used to form both the channels 512 and the thinned portion 114 .
- the middle wafer is secured to a lower wafer at step 908 .
- a material to be dissociated is deposited in at least one of the cavities at step 910 . This could include, for example, depositing the material 116 into the reservoir cavity 108 . Any suitable deposition technique could be used to deposit any suitable material(s) 116 , such as an alkali-based material.
- the top wafer is secured to the middle wafer at step 912 .
- Securing the top wafer 106 to the middle wafer 104 can seal the upper openings of the cavities 108 - 110 and the channels 112 , 512 .
- the cavities and channels in the vapor cell structure can be sealed against the outside environment.
- the material is dissociated to create metal vapor and buffer gas at step 914 .
- This could include, for example, applying UV radiation to the material 116 through the thinned portion 114 of the top wafer 106 .
- This could also include converting at least a portion of the material 116 into the metal vapor and buffer gas. Note, however, that other dissociation techniques could also be used.
- the vapor cell structure can be fabricated in a manner that allows easier dissociation of the material 116 while maintaining the structural integrity of the vapor cell.
- the use of multiple channels can help to ensure that gas can flow into the interrogation cavity 110 , even when one or more channels are blocked.
- FIG. 9 illustrates one example of a method 900 for forming a vapor cell structure
- various changes may be made to FIG. 9 .
- various modifications can be made to the fabrication process.
- various steps in FIG. 9 could overlap, occur in parallel, or occur in a different order.
- top refers to structures in relative positions in the figures and do not impart structural limitations on how a device is manufactured or used.
- secured and its derivatives mean to be attached, either directly or indirectly via another structure.
- the term “or” is inclusive, meaning and/or.
- phrases “associated with,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, have a relationship to or with, or the like.
- the phrase “at least one of,” when used with a list of items, means that different combinations of one or more of the listed items may be used, and only one item in the list may be needed. For example, “at least one of: A, B, and C” includes any of the following combinations: A, B, C, A and B, A and C, B and C, and A and B and C.
Abstract
A first apparatus includes a vapor cell having first and second cavities fluidly connected by multiple channels. The first cavity is configured to receive a material able to dissociate into one or more gases that are contained within the vapor cell. The second cavity is configured to receive the one or more gases. The vapor cell is configured to allow radiation to pass through the second cavity. A second apparatus includes a vapor cell having a first wafer with first and second cavities and a second wafer with one or more channels fluidly connecting the cavities. The first cavity is configured to receive a material able to dissociate into one or more gases that are contained within the vapor cell. The second cavity is configured to receive the one or more gases. The vapor cell is configured to allow radiation to pass through the second cavity.
Description
- This disclosure is generally directed to gas cells. More specifically, this disclosure is directed to a vapor cell structure having cavities connected by channels for micro-fabricated atomic clocks, magnetometers, and other devices.
- Various types of devices operate using radioactive gas or other gas within a gas cell. For example, micro-fabricated atomic clocks (MFACs) and micro-fabricated atomic magnetometers (MFAMs) often include a cavity containing a metal vapor and a buffer gas. In some devices, the metal vapor and the buffer gas are created by dissociating cesium azide (CsN3) into cesium vapor and nitrogen gas (N2).
- This disclosure provides a vapor cell structure having cavities connected by channels for micro-fabricated atomic clocks, magnetometers, and other devices.
- In a first example, an apparatus includes a vapor cell having first and second cavities fluidly connected by multiple channels. The first cavity is configured to receive a material able to dissociate into one or more gases that are contained within the vapor cell. The second cavity is configured to receive the one or more gases. The vapor cell is configured to allow radiation to pass through the second cavity.
- In a second example, a system includes a vapor cell and an illumination source. The vapor cell includes first and second cavities fluidly connected by multiple channels. The first cavity is configured to receive a material able to dissociate into one or more gases that are contained within the vapor cell. The second cavity is configured to receive the one or more gases. The illumination source is configured to direct radiation through the second cavity.
- In a third example, an apparatus includes a vapor cell having a first wafer with first and second cavities and a second wafer with one or more channels fluidly connecting the cavities. The first cavity is configured to receive a material able to dissociate into one or more gases that are contained within the vapor cell. The second cavity is configured to receive the one or more gases. The vapor cell is configured to allow radiation to pass through the second cavity.
- Other technical features may be readily apparent to one skilled in the art from the following figures, descriptions, and claims.
- For a more complete understanding of this disclosure and its features, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which:
-
FIGS. 1 through 4 illustrate an example vapor cell structure in accordance with this disclosure; -
FIGS. 5 and 6 illustrate another example vapor cell structure in accordance with this disclosure; -
FIGS. 7 and 8 illustrate example devices containing at least one vapor cell structure in accordance with this disclosure; and -
FIG. 9 illustrates an example method for forming a vapor cell structure in accordance with this disclosure. -
FIGS. 1 through 9 , discussed below, and the various examples used to describe the principles of the present invention in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the invention. Those skilled in the art will understand that the principles of the present invention may be implemented in any suitable manner and in any type of suitably arranged device or system. -
FIGS. 1 through 4 illustrate an examplevapor cell structure 100 in accordance with this disclosure. Thevapor cell structure 100 can be used, for example, to receive an alkali-based material (such as cesium azide) and to allow dissociation of the alkali-based material into a metal vapor and a buffer gas (such as cesium vapor and nitrogen gas). However, this represents one example use of thevapor cell structure 100. Thevapor cell structure 100 described here could be used in any other suitable manner. - As shown in
FIGS. 1 through 3 , thevapor cell structure 100 includes abottom wafer 102, amiddle wafer 104, and atop wafer 106. Thebottom wafer 102 generally represents a structure on which other components of thevapor cell structure 100 can be placed. Thebottom wafer 102 is also substantially optically transparent to radiation passing through thevapor cell structure 100 during operation of a device, such as a micro-fabricated atomic clock, magnetometer, or other device. Thebottom wafer 102 can be formed from any suitable material(s) and in any suitable manner. Thebottom wafer 102 could, for instance, be formed from borosilicate glass, such as PYREX or BOROFLOAT glass. - The
middle wafer 104 is secured to thebottom wafer 102, such as through bonding. Themiddle wafer 104 includes multiple cavities 108-110 through themiddle wafer 104. Each cavity 108-110 could serve a different purpose in thevapor cell structure 100. For example, thecavity 108 can receive a material to be dissociated, such as cesium azide (CsN3) or other alkali-based material. Thecavity 108 can be referred to as a “reservoir cavity.” Thecavity 110 can receive gas from thecavity 108, such as a metal vapor and a buffer gas. Laser illumination or other illumination could pass through thecavity 110 during operation of a device, such as a micro-fabricated atomic clock, magnetometer, or other device. Thecavity 110 can be referred to as an “interrogation cavity.” -
Multiple channels 112 fluidly connect the cavities 108-110 in thevapor cell structure 100. Eachchannel 112 represents any suitable passageway through which gas or other material(s) can flow. In this example, there are threechannels 112, although thevapor cell structure 100 could include two or more than threechannels 112. Also, thechannels 112 here are generally straight, have equal lengths, and are parallel to one another. However, thechannels 112 could have any other suitable form(s). - The
middle wafer 104 could be formed from any suitable material(s) and in any suitable manner. For example, themiddle wafer 104 could represent a silicon wafer, and the cavities 108-110 and thechannels 112 could be formed in the silicon wafer using one or more wet etches or other suitable processing techniques. As a particular example, thechannels 112 could be formed in a silicon wafer using a potassium hydroxide (KOH) wet etch. The etch of the silicon wafer could also be performed in a self-limiting manner, meaning the etch stops itself at or around a desired depth. For instance, when a narrow mask opening is used to expose the silicon wafer and the etching occurs at a suitable angle (such as about 54.74°), the etching can self-terminate before it etches completely through the silicon wafer. - Each cavity 108-110 and
channel 112 could have any suitable size, shape, and dimensions. Also, the relative sizes of the cavities 108-110 andchannels 112 shown inFIGS. 1 through 3 are for illustration only, and each cavity 108-110 orchannel 112 could have a different size relative to the other cavities or channels. Further, the relative depth of eachchannel 112 compared to the depth(s) of the cavities 108-110 is for illustration only, and each cavity 108-110 andchannel 112 could have any other suitable depth. In addition, while each cavity 108-110 is shown as being formed completely through thewafer 104, each cavity 108-110 could be formed partially through thewafer 104. - The
top wafer 106 is secured to themiddle wafer 104, such as through bonding. Thetop wafer 106 generally represents a structure that caps the cavities 108-110 andchannels 112 of themiddle wafer 104, thereby helping to seal material (such as gas) into thevapor cell structure 100. Thetop wafer 106 is also substantially optically transparent to radiation passing through thevapor cell structure 100 during operation of a device, such as a micro-fabricated atomic clock, magnetometer, or other device. Thetop wafer 106 can be formed from any suitable material(s) and in any suitable manner. Thetop wafer 106 could, for instance, be formed from borosilicate glass, such as PYREX or BOROFLOAT glass. - As shown here, a
portion 114 of thetop wafer 106 could be thinner than the remainder of thetop wafer 106. This may help to facilitate easier UV irradiation of material placed inside thereservoir cavity 108. Note that any wafer 102-106 in thevapor cell structure 100 could have a non-uniform thickness at any desired area(s) of the wafer(s). Also note that theportion 114 of thetop wafer 106 could have any suitable size, shape, and dimensions and could be larger or smaller than thereservoir cavity 108. Theportion 114 of thetop wafer 106 could be thinned in any suitable manner, such as with a wet isotropic etch. - During fabrication of the
vapor cell structure 100, the bottom and middle wafers 102-104 could be secured together, and themiddle wafer 104 can be etched to form the cavities 108-110 and the channels 112 (either before or after the bottom and middle wafers 102-104 are secured together). An alkali-based material 116 (such as cesium azide) or other material(s) can be deposited into thereservoir cavity 108 as shown inFIGS. 3 and 4 . Any suitable deposition technique can be used to deposit the material(s) 116 into thecavity 108. Thetop wafer 106 can be secured to themiddle wafer 104 once the material 116 is placed in thecavity 108. At this point, the cavities 108-110 and thechannels 112 can be sealed. - At least a portion of the material 116 in the
cavity 108 can be dissociated. This could be accomplished by exposing thematerial 116 in thecavity 108 to ultraviolet (UV) radiation. For example, an alkali-basedmaterial 116 can be dissociated into a metal vapor and a buffer gas. As a particular example, cesium azide could be dissociated into cesium vapor and nitrogen gas (N2). Note, however, that other mechanisms could be used to initiate the dissociation, such as thermal dissociation. The dissociation of thematerial 116 creates gas inside thereservoir cavity 108, which can flow into theinterrogation cavity 110 through thechannels 112. - In conventional devices, material is often dissociated in a single cavity, and the resulting gas is kept in the same cavity. Radiation can be passed through the gas in that single cavity during operation of a device, but residue from the original material may still exist in that single cavity. This residue can interfere with the optical properties of the cavity and lead to device failure.
- In accordance with this disclosure, the
material 116 can be placed in onecavity 108 and dissociated, and the resulting gas can be used in adifferent cavity 110 during device operation. As shown inFIG. 4 , anillumination source 118, such as a vertical-cavity surface-emitted laser (“VCSEL”) or other laser, could direct radiation through theinterrogation cavity 110. Even if residue exists in thereservoir cavity 108, it may not interfere with the optical properties in thecavity 110. - The use of
multiple channels 112 also helps to ensure that vapor can travel from thereservoir cavity 108 into theinterrogation cavity 110, even if one ormore channels 112 become blocked by debris or other material(s). In particular embodiments, thechannels 112 could represent self-height-eliminating channels fabricated using a wet etch, rather than a more expensive and time-consuming dry etch. This can help to simplify the manufacture of thevapor cavity structure 100. In addition, thinning theportion 114 of thetop wafer 106 through which UV radiation is directed into thereservoir cavity 108 allows for enhanced dissociation of the material 116 in the cavity 108 (possibly at reduced power levels) while maintaining the mechanical integrity of the overall device. - Although
FIGS. 1 through 4 illustrate one example of avapor cell structure 100, various changes may be made toFIGS. 1 through 4 . For example, thevapor cell structure 100 need not include two cavities and could include three or more cavities. Also, the cavities 108-110 andchannels 112 need not be arranged linearly, and thechannels 112 need not be straight. Any arrangement of cavities connected by channels could be used, including non-linear and multi-level arrangements. Further, thevapor cell structure 100 could be used with any other material(s) and is not limited to alkali-based materials or metal vapors and buffer gases. In addition, thevapor cell structure 100 can be used in any other suitable manner and is not limited to the use shown inFIG. 4 . -
FIGS. 5 and 6 illustrate another examplevapor cell structure 500 in accordance with this disclosure. Thevapor cell structure 500 shown here is similar in structure to that shown inFIGS. 1 through 4 . Reference numerals 102-110 and 114-118 are used here to denote structures that may be the same as or similar to structures described above. In this example, however, channels are not formed in themiddle wafer 104. Rather, one ormore channels 512 are formed in thetop wafer 106. Thetop wafer 106 in this example may be said to represent a “capping” layer since it can be secured to themiddle wafer 104 after thematerial 116 is inserted into thecavity 108, thereby capping thestructure 500. - The channels 512 (and possibly portions of the cavities 108-110) can be etched into the
top wafer 106 in any suitable manner. For example, a photoresist mask can be formed on thetop wafer 106, patterned, and baked/cured. An isotropic wet etch, such as one using a hydrofluoric acid (HF) dip, can then be performed to etch exposed portions of thetop wafer 106. The composition of the wet etch bath and the etch time can be selected to reduce the thickness of thetop wafer 106 as desired. The photoresist layer can then be removed, and thetop wafer 106 can be cleaned in preparation for securing to themiddle wafer 104. In this way, thetop wafer 106 need not be thinned significantly or at all over theinterrogation cavity 110, helping to preserve the mechanical strength of thevapor cell structure 500. Thechannels 512 in the capping layer can also serve other functions, such as by serving as condensation sites in thevapor cell structure 500. -
FIG. 6 illustrates various examples of the channels and cavity portions that can be etched into a capping layer, such as thetop wafer 106. For example,arrangement 602 includes portions of two unequally-sized cavities and a single channel between the cavities. Arrangement 604 includes portions of two unequally-sized cavities and two channels between the cavities.Arrangement 606 includes portions of two equally-sized cavities and three channels between the cavities.Arrangement 608 includes portions of two unequally-sized cavities and four channels between the cavities.Arrangement 610 includes portions of three unequally-sized cavities and five channels coupling each adjacent pair of cavities. Arrangement 612 includes portions of three equally-sized cavities and five channels coupling each adjacent pair of cavities. These arrangements are for illustration only, and other arrangements of cavities and channels (whether linear or non-linear) could be used in thevapor cell structure 500. - In particular embodiments, the
top wafer 106 could be formed from borosilicate glass, and the etch of thetop wafer 106 could occur using a hydrofluoric acid (BHF) bath. A hard mask could be used to mask thetop wafer 106. Any suitable etch, hard mask, and etch depth could also be used. - Although
FIGS. 5 and 6 illustrate another example of avapor cell structure 500, various changes may be made toFIGS. 5 and 6 . For example, thevapor cell structure 500 could include any number of cavities and any number of channels in any suitable arrangement. Also, thevapor cell structure 500 could be used with any suitable material(s) and is not limited to alkali-based materials or metal vapors and buffer gases. In addition, thevapor cell structure 500 can be used in any other suitable manner. -
FIGS. 7 and 8 illustrate example devices containing at least one vapor cell structure in accordance with this disclosure. As shown inFIG. 7 , adevice 700 represents a micro-fabricated atomic clock or other atomic clock. Thedevice 700 here includes one ormore illumination sources 702 and avapor cell 704. Eachillumination source 702 includes any suitable structure for generating radiation, which is directed through thevapor cell 704. Eachillumination source 702 could, for example, include a laser or lamp. - The
vapor cell 704 represents a vapor cell structure, such as thevapor cell structure interrogation cavity 110 of thevapor cell 704 and interacts with the metal vapor. The radiation can also interact with one or more photodetectors that measure the radiation passing through theinterrogation cavity 110. For example, photodetectors can measure radiation from one or more lasers or lamps. - Signals from the photodetectors are provided to
clock generation circuitry 706, which uses the signals to generate a clock signal. When the metal vapor is, for example, rubidium 87 or cesium 133, the signal generated by theclock generation circuitry 706 could represent a highly-accurate clock. The signals from the photodetectors are also provided to acontroller 708, which controls operation of the illumination source(s) 702. Thecontroller 708 helps to ensure closed-loop stabilization of the atomic clock. - As shown in
FIG. 8 , adevice 800 represents a micro-fabricated atomic magnetometer or other atomic magnetometer. Thedevice 800 here includes one ormore illumination sources 802 and avapor cell 804. Eachillumination source 802 includes any suitable structure for generating radiation, which is directed through thevapor cell 804. Eachillumination source 802 could, for example, include a laser or lamp. - The
vapor cell 804 represents a vapor cell structure, such as thevapor cell structure interrogation cavity 110 of thevapor cell 804 and interact with the metal vapor. The radiation can also interact with one or more photodetectors that measure the radiation passing through theinterrogation cavity 110. For example, photodetector(s) can measure radiation from one or more lasers or lamps. - Signals from the photodetector(s) are provided to a
magnetic field calculator 806, which uses the signals to measure a magnetic field passing through theinterrogation cavity 110. Themagnetic field calculator 806 here is capable of measuring extremely small magnetic fields. The signals from the photodetector(s) can also be provided to acontroller 808, which controls operation of the illumination source(s) 802. - Although
FIGS. 7 and 8 illustrate examples ofdevices FIGS. 7 and 8 . For example, thedevices FIGS. 7 and 8 have been simplified in order to illustrate example uses of thevapor cell structures -
FIG. 9 illustrates anexample method 900 for forming a vapor cell structure in accordance with this disclosure. As shown inFIG. 9 , multiple cavities are formed in a middle wafer of a vapor cell structure atstep 902. This could include, for example, forming cavities 108-110 in a silicon wafer or othermiddle wafer 104. Any suitable technique could be used to form the cavities, such as a wet or dry etch. - One or more channels are formed in the middle wafer or a top wafer of the vapor cell structure at
step 904. This could include, for example, forming one ormore channels 112 in the silicon wafer or othermiddle wafer 104. This could also include forming one ormore channels 512 in thetop wafer 106 or other capping layer. Any suitable technique could be used to form the channels, such as a wet etch. The formation of the cavities and channels could also overlap, such as when the same etch is used to form both the cavities 108-110 and thechannels 112. - A portion of the top wafer is thinned at
step 906. This could include, for example, etching aportion 114 of thetop wafer 106 in an area adjacent to thereservoir cavity 108. Any suitable etch can occur here, such as an isotropic wet etch. The formation of channels in the top wafer and the thinning of the top wafer could also overlap, such as when the same etch is used to form both thechannels 512 and the thinnedportion 114. - The middle wafer is secured to a lower wafer at
step 908. This could include, for example, bonding themiddle wafer 104 to thebottom wafer 102. If the cavities 108-110 are formed completely through themiddle wafer 104, securing themiddle wafer 104 to thebottom wafer 102 can seal the lower openings of the cavities 108-110. - A material to be dissociated is deposited in at least one of the cavities at
step 910. This could include, for example, depositing thematerial 116 into thereservoir cavity 108. Any suitable deposition technique could be used to deposit any suitable material(s) 116, such as an alkali-based material. - The top wafer is secured to the middle wafer at
step 912. This could include, for example, bonding thetop wafer 106 to themiddle wafer 104. Securing thetop wafer 106 to themiddle wafer 104 can seal the upper openings of the cavities 108-110 and thechannels - The material is dissociated to create metal vapor and buffer gas at
step 914. This could include, for example, applying UV radiation to thematerial 116 through the thinnedportion 114 of thetop wafer 106. This could also include converting at least a portion of the material 116 into the metal vapor and buffer gas. Note, however, that other dissociation techniques could also be used. - In this way, the vapor cell structure can be fabricated in a manner that allows easier dissociation of the
material 116 while maintaining the structural integrity of the vapor cell. Moreover, the use of multiple channels can help to ensure that gas can flow into theinterrogation cavity 110, even when one or more channels are blocked. - Although
FIG. 9 illustrates one example of amethod 900 for forming a vapor cell structure, various changes may be made toFIG. 9 . For example, as noted above, various modifications can be made to the fabrication process. Also, while shown as a series of steps, various steps inFIG. 9 could overlap, occur in parallel, or occur in a different order. - It may be advantageous to set forth definitions of certain words and phrases used throughout this patent document. The terms “top,” “middle,” and “bottom” refer to structures in relative positions in the figures and do not impart structural limitations on how a device is manufactured or used. The term “secured” and its derivatives mean to be attached, either directly or indirectly via another structure. The terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation. The term “or” is inclusive, meaning and/or. The phrase “associated with,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, have a relationship to or with, or the like. The phrase “at least one of,” when used with a list of items, means that different combinations of one or more of the listed items may be used, and only one item in the list may be needed. For example, “at least one of: A, B, and C” includes any of the following combinations: A, B, C, A and B, A and C, B and C, and A and B and C.
- While this disclosure has described certain embodiments and generally associated methods, alterations and permutations of these embodiments and methods will be apparent to those skilled in the art. Accordingly, the above description of example embodiments does not define or constrain this disclosure. Other changes, substitutions, and alterations are also possible without departing from the spirit and scope of this disclosure, as defined by the following claims.
Claims (20)
1. An apparatus comprising:
a vapor cell having first and second cavities fluidly connected by multiple channels;
the first cavity configured to receive a material able to dissociate into one or more gases that are contained within the vapor cell; and
the second cavity configured to receive the one or more gases;
wherein the vapor cell is configured to allow radiation to pass through the second cavity.
2. The apparatus of claim 1 , wherein the vapor cell comprises:
a first wafer comprising the cavities and the channels.
3. The apparatus of claim 2 , wherein the vapor cell further comprises:
at least one second wafer secured to the first wafer, the at least one second wafer sealing ends of the cavities and the channels.
4. The apparatus of claim 2 , wherein:
the vapor cell further comprises a second wafer secured to the first wafer; and
the second wafer is thinner in a location proximate to the first cavity.
5. The apparatus of claim 1 , wherein the vapor cell comprises:
a first wafer comprising the cavities; and
a second wafer secured to the first wafer, the second wafer comprising the channels.
6. The apparatus of claim 1 , wherein the material comprises an alkali-based material able to dissociate into a metal vapor and a buffer gas.
7. The apparatus of claim 6 , wherein the material comprises cesium azide (CsN3) and is able to dissociate into cesium vapor and nitrogen gas (N2).
8. A system comprising:
a vapor cell comprising:
first and second cavities fluidly connected by multiple channels;
the first cavity configured to receive a material able to dissociate into one or more gases that are contained within the vapor cell; and
the second cavity configured to receive the one or more gases; and
an illumination source configured to direct radiation through the second cavity.
9. The system of claim 8 , wherein the vapor cell comprises:
a first wafer comprising the cavities and the channels.
10. The system of claim 9 , wherein the vapor cell further comprises:
at least one second wafer secured to the first wafer, the at least one second wafer sealing ends of the cavities and the channels.
11. The system of claim 9 , wherein:
the vapor cell further comprises a second wafer secured to the first wafer; and
the second wafer is thinner in a location proximate to the first cavity.
12. The system of claim 8 , wherein the vapor cell comprises:
a first wafer comprising the cavities; and
a second wafer secured to the first wafer, the second wafer comprising the channels.
13. The system of claim 8 , wherein the material comprises an alkali-based material able to dissociate into a metal vapor and a buffer gas.
14. The system of claim 13 , wherein the material comprises cesium azide (CsN3) and is able to dissociate into cesium vapor and nitrogen gas (N2).
15. The system of claim 8 , further comprising:
clock generation circuitry configured to generate a clock signal based on the radiation directed through the second cavity.
16. The system of claim 8 , further comprising:
a magnetic field calculator configured to determine a measurement of a magnetic field through the vapor cell based on the radiation directed through the second cavity.
17. An apparatus comprising:
a vapor cell having a first wafer comprising first and second cavities and a second wafer comprising one or more channels fluidly connecting the cavities;
the first cavity configured to receive a material able to dissociate into one or more gases that are contained within the vapor cell; and
the second cavity configured to receive the one or more gases;
wherein the vapor cell is configured to allow radiation to pass through the second cavity.
18. The apparatus of claim 17 , wherein the vapor cell further comprises:
a third wafer secured to the first wafer, the third wafer sealing ends of the cavities.
19. The apparatus of claim 17 , wherein the second wafer is thinner in a location proximate to the first cavity.
20. The apparatus of claim 17 , wherein the material comprises an alkali-based material able to dissociate into a metal vapor and a buffer gas.
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CN201410347317.2A CN104345634A (en) | 2013-07-23 | 2014-07-21 | Vapor cell structure having cavities connected by channels for micro-fabricated atomic clocks, magnetometers, and other devices |
US15/430,797 US10024929B2 (en) | 2013-07-23 | 2017-02-13 | Vapor cell structure having cavities connected by channels for micro-fabricated atomic clocks, magnetometers, and other devices |
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